Interestingly enough, the rumor of the cancellation was confirmed by Marvel's main pr site, Comic Book Resources.

Now at this weekend's comic book convention in NYC, Marvel's Senior Vice President of Publishing and head editor, Tom Brevoort, stated Fantastic Four will still be published in 2015 (the Fantastic Four movie's release), but offered that by the month of May it could potentially be cancelled to due their big "Time Runs Out" event (via Newsarama).

I'm going to publish it. It will have four characters in it! I presume that James Robinson will write that all the way into the future. At least until Time Runs Out, then anything can happen.